Alijan

Whether or not to provide evidence of an engagement party would be for the K-1 visa interview, and would depend on what is culturally normal for that country.
Getting the I-129F petition approved only requires that you are both free to marry at the time of filing and that you have been together in person within the 2 years prior to filing. Getting the petition approved is not really a challenge. It should not be forgotten that following the I-129F petition, the foreign fiance(e) will apply for a K-1 visa at the consulate in their country. The K-1 visa interview is where the relationship will be vetted and the CO will look at their case and decide if they have a real relationship or one that is just for immigration purposes only.
They will need to have plenty of proof to show that they did not simply get their US citizenship so they could bring over someone else from their country. The COs know all about how that works and watch out for things like that. The poster above that talks about extra scrutiny is absolutely correct. They should be aware of that and be prepared for it. I suggest the OP does some reading in the Middle East and North Africa(MENA) regional forum in order to prepare for the K-1 visa interview to come.

To the OP. Remember, there are two major phases of the K1 process. During the initial submission of the application, the USCIS will initiate background checks on both the petitioner and beneficiary. They will also look at the evidence to see whether you are both free to marry as of the date of filing. For this you must submit evidence of divorce using a copy of the divorce decree, or certified certificate of divorce. After the petition is approved it will move to the second stage of the process, which requires more detail about the beneficiary.
Second stage after approval
As another poster passionately commented, countries like Afghanistan will receive more scrutiny that other countries due to a high-incidence of fraud and US national security. For this reason it will be very important for you to carefully document the evolution of your relationship. You must show that you maintain contact and provide evidence in the form of phone records, photos, receipts, email, and so on. Just knowing something in your heart is not evidence enough. Focus on how your relationship has evolved since the date of your divorce.

There is no 'legal' requirement, but he will most certainly have a difficult time...which is all I was saying. In his K1 petition he will have to show his divorce documents, plus his engagement which was prior to divorce and right at the time he was getting citizenship...plus Afghanistan is a high-fraud country. USCIS will take their time reviewing this to make sure it's not a fraudulent relationship.
He also hasn't shared any information other than he's engaged. Alijan, if you have significant proof of your relationship with the fiancée and its valid, you should not worry and go ahead and file. If you're speaking in terms of technicality, USCIS only "requires" you having met in person and been face to face one time within the last 2 years, which according to you was September 2013, so good luck to you. inshaAllah it will work out.

There is no legal requirement that you must be single when you first meet. The requirement is to have met within the previous two years, and that as of the date of filing for K1 that you are legally free to marry. Avoid engagement parties and celebrations as they may be viewed as a marriage. Present only the evidence of having met face to face.

you can not lie to the CO or if you was not sure should say Im not sure because once they fund out is not true ...they wont believe anything so get advice from a lawyer plz ASP..Allah with you...there always a solution when you pray Allah...

listen dude, your issue has nothing to do with Islam !!!
I am wondering why are you trying to talk about religion?? and criticizing Islam will not get you a GC.
if you have an asylum case that would be acceptable to talk about your religion issue, taking into consideration you need to respect the others religion whatever it's.
At the beginning you were picturing your marriage is ideal. However, later on you started talking about your bipolar wife and finally you would do anything to get a your ROC approved.
I will try to forget your metaphoric description which you tried to link Islam with terrorism, and I will give you my best honest advice.
since you r an educated person, first thing to do is to analyze the problem. most of people got their ROC approved without an interview. however, you need to submit tons of document to show the joint life. when USCIS sent the application back to the local field office, it reflects that USCIS has a fraud suspicions[ remember when you applied for the GC they had to conduct an interview in order to proof the genuinity of the relationship].
you need to do your best to get your wife her for the interview, and choose a good time to talk to your wife about this issue. if she said no, explain the situation and ask her straight up if she cares about your immigration issue or not[ Are u willing to co-operate to finish my ROC ,ask her]. if she does, she can write a letter to IO in order to reschedule the interview and take that letter with you when you go to the inforpass. Let her explain everything, her internship situation and the financial issue... etc.. so after she completes her program she can come and make the things going.
however, if your wife has decided to move overseas without you and she is not willing to cooperate . I think you need a lawyer, the problem is you filed the application jointly and in realty it's not, since your wife is not willing to show up, . I am not gonna assume anything. but, since the application was filed jointly the IO will not approved and one of the parties is not present except if he/she is deployed. if I were you I would consult an experienced lawyer, don't gamble with this.

Dear Dlodi if your marriage is genuine then y are you worrying. And 1 thing which i don't quiet understand is why are you saying in almost every post that you left islam and getting threats and stuff. Religion has got nothing to do with ur immigration status. If your marriage in genuine you should be here proving that in your posts rather than putting focus on the fact that they should let you stay because you left islam.

There is a saying "There are no second chances in life, except to feel remorse", then call your wife and ask her to flight back to USA to attend the interview,period.Don't be a person who has to look back and wonder what you would have or could have had, take action NOW.
You said se is bipolar, but being bipolar does not justify her abuse against you, or she manages to take her medications correctly or man move on.Good luck.